Small, portable printers for use with computers have become very desirable with the advent of portable computers such as the lap top computers and terminals. Naturally, and since such printers are intended to be portable, it is highly desirable that they be as small and light as possible. Furthermore, the computer business is extremely competitive and the reduction in sales price by price saving during manufacture of the printer is of major significance.
In addition to the foregoing, the advance in the printer art has demanded that such printers be more and more accurate and that they produce not only high quality characters, but that the graphics produced thereby have the very best high definition.
For the most part, the portable printers have been of the dot matrix type which includes mechanical, pin-type printers, thermal printers, or ink jet printers. Among these, an ink jet printer, referred to as a "Think Jet" manufactured by Hewlett Packard has proved to be very successful since it is light weight, relatively low in cost, and totally portable.
In ink jet printers, the letters or graphics are formed by the disposition of ink that is sprayed or spurted onto the paper. There is no mechanical impact such as is true of the mechanical pin-type printers. Accordingly, it has been possible to eliminate the need for a heavy, large platen that is required to absorb the mechanical impact that occurs during the transfer of the characters to paper.
As a result of the accuracy demanded, the printers have certain problems in common. For example, accuracy and repeatability of paper feed when advancing the paper is required. Paper feed accuracy may be affected if there is backlash in the mechanism driving the paper through the printer. Also, a problem that has to be considered in the design of such printers is the necessity for locating the position of the print head vertically with respect to the paper feed. For example, to avoid printing into a lower or upper margin, or, printing over the perforations in continuous feed forms, it is necessary to know where the print head is located vertically so that the printer will skip to the next page or form and begin printing at the appropriate position.
One other problem encountered in the manufacture of portable printers, is the weight of the printer itself. It is highly desirable to reduce all stresses within the printer to be able to reduce the number of structural members that are required to provide a rigid chassis for supporting the paper, paper advance mechanism and the print head and to maintain those devices in their relative positions to maintain printer accuracy.
In addition to the foregoing problems, it is highly desirable in a portable printer to be able to print on individual sheets, rolled paper or on continuous feed form paper. Manifestly, such an arrangement can be provided, but the complexity, weight and cost of such mechanism must be suitable for use in a portable printer.